Apparatus and process for the abatement of semiconductor manufacturing effluents containing fluorine gas

ABSTRACT

Apparatus and process for the abatement of fluorine and fluorine-containing compounds from gases containing same, such as effluent gas streams from semiconductor manufacturing operations, wherein a fluorocompound abatement medium is injected into the fluorocompound-containing gas. The fluorocompound abatement medium comprises at least one of steam, methane and hydrogen, with the proviso that when the fluorocompound abatement medium contains methane and/or hydrogen, the injection of the fluorocompound abatement medium is conducted under non-combustion conditions.

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 11/151,061, filed Jun. 13, 2005, which is adivision of and claims priority to U.S. patent application Ser. No.09/551,279, filed Apr. 18, 2000, now U.S. Pat. No. 6,905,663 issued Jun.14, 2005. Each of these applications is hereby incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

This invention relates to an apparatus and process for abatement offluorine in gases containing same, as for example in effluent gasstreams produced in semiconductor manufacturing operations.

DESCRIPTION OF THE RELATED ART

The trend of recent years in the semiconductor industry has been tooptimize reactors that use perfluorinated compounds (PFCs), as anapproach to minimizing the presence of PFCs in the effluents of suchreactor systems.

Despite the pervasiveness of this approach, there is also emerging arenewed effort to resolve the problem of PFC emissions by treatment ofeffluent gas streams from such reactor systems, to remove highconcentrations of fluorine gas and other fluorinated organic gases fromthe effluent gas streams that are discharged from the reactor or otherprocess tool.

In December 1997, over 160 countries of the world negotiated the KyotoClimate Protection Protocol. This global agreement is intended toencourage immediate efforts to reduce the emission of greenhouse gases.Perfluorinated gases and sulfur hexafluoride (SF₆) were listed among thesix gases specifically targeted under the protocol. These fluorine (F)saturated species are among the strongest greenhouse gases, with globalwarming potentials (GWPs) 3 and 4 orders of magnitude higher than CO₂.Moreover, they are extremely stable molecules with lifetimes in theatmosphere of thousands of years.

The electronics industry uses PFCs in a number of plasma processes togenerate highly reactive F₂ and fluorine radicals. These in situgenerated species are produced to remove residue from tools or to etchthin films. The most commonly used PFCs include CF₄, C₂F₆, SF₆, C₃F, andNF₃. Chamber cleans after chemical vapor deposition (CVD) processesaccount for 60-95% of PFC use (Langan, J., Maroulis, J., and Ridgeway,R. Solid State Technology July, 115 (1996)).

Ongoing research to reduce PFC emission levels falls into fourcategories: optimization, alternative chemicals, recovery/recycle, andabatement. Process optimization was recognized by industry leaders asthe preferred choice to reduce PFC emissions; abatement fell last onthat list.

Process optimization involves adjusting the operating conditions in thereactor to achieve enhanced PFC conversion within the tool. Existingnon-optimized conditions result in PFC utilization that vary dependingon the specific gas and process used. For instance, oxide etch using acombination of CF₄ and CHF₃ ranks lowest with 15% efficiency. Tungstendeposition processes are reported to utilize up to 68% of NF₃. Recentdevelopments in optimized plasma clean technologies were proven toprovide up to 99% NF₃ utilization within the tool (Proceedings of theGlobal Semiconductor Industry Conference on Perfluorocarbon EmissionsControl, Monterey, Calif. Apr. 7 and 8, 1998).

High PFC conversions result inevitably in the formation of hazardous airpollutants (HAPs). Breakdown products include mostly fluorine (F₂) andsilicon tetrafluoride (SiF₄) gases and to a lesser extent HF and COF₂.Destruction of fully fluorinated gases generates considerably augmentedHAP yields compared to the initial PFC volumes delivered to the tool.For instance, assuming stoichiometric conversion of PFCs into F₂, a 1liter per minute (lpm) flow rate of NF₃ could potentially produce 1.5lpm of F₂. The combined exhaust stream of four chambers couldpotentially generate up to 6 lpm of fluorine gas resulting in apost-pump effluent concentration of 3% F₂ (50 lpm ballast N₂ per pump).These estimated values double with hexafluorinated PFCs (compared toNF₃) and are likely to increase in the future with the projectedthroughputs of 300 mm wafer manufacturing.

The toxic and corrosive nature of fluorinated HAPs pose considerablehealth and environmental hazards in addition to jeopardizing theintegrity of exhaust systems. In particular, the oxidizing power of F₂is unmatched by any other compound and is far more reactive than otherhalogens. The large volumes of F₂ and other fluorinated hazardousinorganic gases released during optimized plasma processing require theuse of (POU) abatement devices in order to minimize potential dangersand to prolong tool operation. Out of all fluorinated inorganic gases,fluorine gas, F₂, poses the higher challenge for its abatement and theensuing description addresses existing alternatives for its abatement.

Current fluorine abatement alternatives include dilution, dry, thermaland wet techniques.

In dilution treatment, non-reactive gases are added to lower theconcentration of fluorine and other hazardous materials in the effluentstream being treated.

At high concentrations, fluorine reacts exothermically with all elementsexcept O₂, N₂, and noble gases. Consequently, a reasonable approach toF₂ abatement is to remove this highly active gas using naturallyoccurring reactions without adding energy to the system.

In the dry abatement methods for F₂ removal, the fluorine gas stream isflowed through a dry bed filled with a reactive material. Alumina hasbeen used in the past for this purpose (J. T. Holmes et. al. I&ECProcess Design and Development, Vol 6, No. 4, pg 411 (1967)). In thisapproach, suitable dry chemicals convert F₂ into innocuous solids orbenign gases without generating excessive heat, an important conditionsince heat generation can be a limiting factor especially if the drychemical bed is exposed to large volumes of F₂.

Thermal abatement approaches combine reactive materials and F₂ inside areactor that is heated using fuel or electrical energy. Existing thermalunits require the addition of hydrogen source/fuels such as methane orhydrogen to drive the fluorine reaction to completion, convertingfluorine into HF. Users do not desire adding such gases since theythereby increase hazard risk and cost of ownership of the abatementsystem. Further, the by-products generated by the thermal abatement ofF₂ typically include hot acids that in turn require the use of apost-treatment water scrubber. The removal efficiencies in thesescrubbers are often compromised due to the fact that the scrubbingefficiency of most acid gases decreases as a function of increasingtemperature. In addition, containment of hot concentrated acids requiresexpensive materials of construction to prevent temperature-enhancedcorrosive attack on lines, vessels and fittings.

In wet abatement methods, the fluorine is reacted with H₂O. The mainproducts of the reaction between water and F₂ are HF, O₂, and H₂O₂.(Cady, G. H. J. J. Am. Chem. Soc. 57, 246 (1935). Objections to usingwater scrubbers include concerns over the formation of unwanted OF₂, andthe large water consumption necessary to achieve acceptable removalefficiencies at high fluorine challenges.

It therefore is apparent that all of the conventionally employedapproaches to abating fluorine in effluent gas streams have associateddeficiencies, which limit their commercial viability and amenability toeconomic and practical use.

It correspondingly is an object of the present invention to provide animproved apparatus and method for the removal of fluorine andfluorine-containing gaseous compounds from gases containing same.

It is another object of the invention to provide an improved apparatusand method of such type that is adaptable to implementation for thetreatment of effluent gas streams from semiconductor manufacturingoperations.

Other objects and advantages of the invention will be more fullyapparent from the ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

The present invention relates to an apparatus and method for abatinggaseous fluorocompounds (such term being used herein to include gaseousfluorine and/or other fluorine-containing gaseous compounds, e.g., F₂and fluorine radicals, from gases containing such fluorocompounds.

In one aspect, the present invention relates to a process for abatementof gaseous fluorocompounds in a gas containing same. Such processcomprises injecting a fluorocompound abatement medium into thefluorocompound-containing gas, wherein the fluorocompound abatementmedium comprises at least one of steam, methane and hydrogen, optionallyin further combination with a catalyst effective to enhance theabatement, with the proviso that when the fluorocompound abatementmedium contains methane and/or hydrogen, the injection of thefluorocompound abatement medium is conducted under non-combustionconditions.

In another aspect, the invention relates to a process for abatement ofgaseous fluorocompounds in a gas containing same, said processcomprising injecting a fluorocompound abatement medium into thefluorocompound-containing gas, wherein the fluorocompound abatementmedium comprises at least one hydrocarbon gas and the injection of thefluorocompound abatement medium is conducted under non-combustionconditions.

A further aspect of the invention relates to a steam injectionfluorocompound abatement apparatus comprising:

an elongate flow passage member adapted for introduction offluorocompound-containing gas thereto at a first end thereof for flowthrough the flow passage member to a second discharge end thereof;

a heat source for heating the fluorocompound-containing gas during flowthrough the elongate flow passage member to a reaction zone at anintermediate portion of the elongate flow passage member between itsfirst and second ends; and

a steam source arranged to inject steam into the reaction zone of theelongate flow passage member.

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of an apparatus for steam injection abatementof fluorine according to one embodiment of the invention.

FIG. 2 is a side elevation view of the apparatus of FIG. 1.

FIG. 3 is a graphical representation of the product distribution for thereaction between methane and fluorine gas.

FIG. 4 is a graph of fluorine destruction as measured by effluentfluorine concentration, in ppm, at the exhaust of the treatmentfacility, as a function of hydrogen flow rate, in standard liters perminute.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

The present invention relates to the discovery that injection of steam,hydrogen, and methane may be efficiently and advantageously used toabate fluorine and fluorine-containing compounds from gases containingsame.

Steam injection has been employed in prior efforts to treat gas streams.An apparatus built by E.I. du Pont de Nemours, Inc. to abate fluorinegas in chemical process plants was described in 1954 (Smiley, S. H. andSchmitt, C. R. Ind. Eng. Chem., 46, pg 244 (1954)) and in a follow-uppaper in 1962 (Streng A. G. Combustion Flame, 6, pg 89 (1962)). Thepresent invention is a departure from this prior work, and utilizessteam injection based on the specific requirements and conditions ofpoint-of-use abatement of fluorine and fluorine-containing gases insemiconductor effluent streams.

Under certain conditions, steam reacts with a preheated flow containingfluorine gas to form HF, with the extent of the reaction being highlydependent on the initial concentration of fluorine in the fluorine gasstream, the gas temperature, and the volume of steam injected.

FIG. 1 is a top plan view and FIG. 2 is a side elevation view of aschematically rendered steam injection apparatus 10 according to oneembodiment of the invention, for abatement of fluorine gaseousconstituent(s) in a gas stream 12 containing such constituent(s).

Referring now to FIG. 1, the system consists of a gas preheating stage6, in which the fluorine-containing gas 12 is flowed into the gas flowpassage 24 bounded by passage wall 22 in aluminum block 14. The aluminumblock 14 is formed in two half-sections 16 and 18.

Each of the half sections has respective channels therein that uponmating of the half-sections forms a first throughbore for passage of awater line 26 therethrough, and a second throughbore for installation ofa cartridge heater 20 therein. The aluminum block 14 therefore forms anassembly that is readily assembled and disassembled, by use of suitablemeans (not shown in FIGS. 1 and 2) for disengageably engaging therespective half-sections to one another. Such means may for examplecomprise mechanical fasteners, hinges, clasps, set screws, keying orlock structures, integrally formed connectors on each half-section, etc.

The pre-heat stage 6 thus includes an extended length flow path throughwhich the gas stream flows to the reaction stage 7 of the apparatus,while the water line 26 carries water from a suitable source (not shown)for heating by the cartridge heater 20 to generate stream.

The thus-generated steam then is introduced to the gas flow passage 24at steam entrance 30, at an intermediate section of the passage. Thesteam then mixes and reacts with the fluorine constituent(s) of the gasstream.

The heat of the reaction then is dissipated by heat exchange coolingcoils 32 helically circumscribing the cooling stage 8 portion of thepassage 24. The gas stream during its flow through the passage is cooledto a suitable discharge temperature and exhausted from the passage atthe exhaust 9.

The optional cooling stage 8 functions to quench the gas stream tosuitable temperature after the reaction. Pre-heating the gas stream forthe steam reaction can be accomplished in a number of ways, such asusing the cartridge heater/metal block combination illustratively shown,or by any other suitable means.

Steam can be generated using the same heating source used to increasethe temperature of the gas stream or using an independent steamgenerator. The quench region may be desirable if the effluent gases aredelivered into an additional scrubbing system requiring the stream to becooled.

The following Table 1 summarizes experimental results injectingsuperheated steam (300 F., 60 psig) to a varying concentration of aheated stream containing fluorine gas. These results were generated bydelivering the steam into the oxidizer of an EcoCVD™ electrothermaloxidizer abatement device, commercially available from ATMI EcosysCorporation, San Jose, Calif. Table 1 below summarizes results for theabatement (destruction and removal efficiency, % DRE) of F₂. TABLE 1 F₂abatement injecting steam into the oxidizer of the EcoCVD ™ Unit TotProc N2 Tot F2 in F2 inlet HF Out F2 Out slpm slpm (ppm) (ppm) (ppm) F2% DRE 220 2.5 11364 252 1041 90.84 190 2.5 13158 365 694 94.72 130 2.519231 379 128 99.34 130 3 23077 533 128 99.44 130 4 30769 462 67 99.78

Table 1 shows the DRE levels for F₂ to be at least 90% in all runs.

It is to be recognized that steam injection can be used in combinationwith a catalyst to enhance the destruction efficiency of the fluorinegas and fluorine-containing gaseous constituents of the gas stream. Suchcatalysts can include (among others) metals, spark generating devices,glow plugs, hydrogen, ammonia, hydrogen peroxide, reducing agents,bases, or any catalytically active organic compounds.

1. The fluorocompound abatement process of the invention may be carriedout at any suitable process conditions, with the proviso that whenhydrocarbon gases (e.g., methane) and/or hydrogen are used as thefluorocompound abatement medium, such abatement conditions do notencompass or mediate combustion of the fluorocompound abatement medium.The choice of appropriate process conditions will depend on the specificfluorocompound abatement medium employed, and may be readily determinedwithin the skill of the art, without undue experimentation. For example,such non-combustion abatement conditions may include a temperature inthe range of from about 120 to 300° F.

Experimental results have demonstrated that steam doped with a 1:36volume ratio between isopropyl alcohol (an organic compound) and waterabated 2.5 slpm F₂ in 220 slpm N₂ to less than 1 ppm. In general, theconcentration of catalyst is desirably in the range of 2 to 15% byvolume, based on the volume of water (at standard temperature andpressure conditions of 25° C. and 1 atmosphere pressure, respectively),and more preferably in the range of from about 2.5 to about 7% byvolume, based on the volume of water.

The foregoing results show that the use of steam in combination with anaqueous alkanolic solution is highly efficacious to reduce the fluorinecontent of the effluent gas stream containing fluorine or other gaseousfluorine-containing compounds.

Methane injection is another methodology that may be employed in thepractice of the invention to abate fluorine constituents of effluent gasstreams containing same.

The methane may be injected into a heated zone to abate a stream offluorine gas, or the fluorine or fluorine-containing gaseous compoundsof a gas stream containing same. Existing methods of abatement whichutilize methane to generate heat (via combustion with oxygen or air),utilize 50 times the volume of methane used in a representativeembodiment of the present invention. In accordance with this aspect ofthe invention, methane behaves solely as a reaction catalyst while heatis produced using electrical means (not combustion). This distinction isan important one, inasmuch as the cost of methane compared to prior artmethane combustion systems is reduced by fifty times in theaforementioned representative embodiment.

Experimental results involving 3 slpm F₂ in 220 slpm N₂ in a 1650° F.reactor required 1.2 slpm of methane to achieve complete F₂ destruction.The chart in FIG. 3 illustrates the reaction by-products generated bythe reaction between methane and fluorine gas: 50% CO₂, 2% CF₄, 13%CH₂F₂, 12% CH₃F, 12% CH₄, 2% CHF₃ and 9% CO, wherein all percentages areby weight, based on the total weight of the reaction products. Out of850 sccm CH₄ introduced to the F₂ abatement system, only 12 sccm of CF₄were formed. These results show the efficacy of the invention involvingthe mixing and reaction of methane and fluorine gas with one anotherunder non-combustion conditions. In the practice of this aspect of theinvention, the appropriate proportions of the methane and fluorineconstituents of the reaction mixture are readily determinable withoutundue experimentation, by stoichiometric and thermodynamic analysis forthe specific gas composition being treated in the abatement process ofthe invention.

It therefore is to be recognized that, while the described invention wassuccessful in destroying fluorine using methane, small volumes of otherorganic species (other than methane) would behave similarly. Theseorganic species could include other hydrocarbon gases (ethane, propane,butane, etc.) in addition to organic liquids, and solid organic sources.In general, however, because of cost and “cleanliness” of the reactioninvolved, methane is highly preferred.

Hydrogen injection may be employed in another aspect of the inventionfor the abatement of fluorine and fluorine-containing gas components ina gas composition containing same.

This aspect of the present invention involves the injection of hydrogento a heated reactor to convert fluorine to hydrogen fluoride. Thismethod has the advantage over the use of methane, in that it does notgenerate organic fluorinated species. The volume of H₂ introduced ishighly dependent on the overall gas flow rate of the stream to be abatedand fluorine content within the stream. FIG. 4 demonstrates the volumeof hydrogen necessary to achieve complete F₂ destruction. These resultswere generated using hydrogen injection in the oxidizer of an EcoCVD™electrothermal oxidation system, challenged with 160 or 220 slpm N₂mixed with 1, 2.5, and 4 slpm F₂.

In the injection of hydrogen gas for the abatement of the fluorineand/or fluorine-containing components of a process gas composition, thehydrogen is reacted with the fluorine components under non-combustionconditions, as again may be readily determinable within the skill of theart without undue experimentation, by the expedient of stoichiometricand thermodynamic analysis, and routine experimentation.

The results of FIG. 4 indicate that more hydrogen is required when theinitial challenge contains less fluorine gas, and at lower residencetimes (higher overall flow rates). In nearly all cases, completedestruction was achieved when using between 5 and 8 slpm of hydrogengas.

It should be recognized that hydrogen can be either provided from anexternal source or generated in-situ using hydrogen generating sourcessuch as an electrolytic hydrogen generator, or a chemical generator ofhydrogen.

The present invention thus provides a simple and effective approach tothe problem of F₂ and fluorine-containing compounds reduction in gasstreams or gas volumes containing same. The approaches that may beemployed are: addition to the fluorine-containing gas of methane,wherein the methane is used to abate the fluorine-containing gas or toform certain perfluoro compounds; low flow introduction of hydrogen tothe fluorine-containing gas, under non-combustion conditions; contactingthe fluorine-containing gas with alternative atomic hydrogen sources;contacting the fluorine-containing gas with steam in the presence of achemical “catalyst” (any of a variety of species); injection of a“chemical catalyst;” and the use of oxidation catalysts to oxidize thefluorine content of the gas.

The methods of the present invention in addition to abating fluorinecomponents of the gas containing same, are also able to abatepyrophorics and flammable constituents in the gas when present therein.Examples of such pyrophoric, flammable constituents include silanes,phosphine, etc.

The apparatus and method of the present invention thus provide multipleapproaches for the abatement of fluorine gas from gas streams containingsame.

The preferred abatement media of the present invention are steam,hydrogen and methane. These injected agents may be used singly or incombinations, or in single treatment fashion followed by combinatorialtreatment (e.g., by initial steam injection, followed by combinedhydrogen and methane injection at a downstream site from the steaminjection locus in the flow path of the gas stream).

Further, while the invention is preferred to be employed in theabatement of fluorine and gaseous fluorine-containing gaseous species ina gas stream containing same, the gas treatment may be directed to astatic volume of gas, so that the treatment is carried out in batch orsemi-batch fashion.

Although the invention has been variously disclosed herein withreference to illustrative embodiments and features, it will beappreciated that the embodiments and features described hereinabove arenot intended to limit the invention, and that other variations,modifications and other embodiments will suggest themselves to those ofordinary skill in the art. The invention therefore is to be broadlyconstrued, consistent with the claims hereafter set forth.

1. A steam injection fluorocompound abatement apparatus comprising: anelongate flow passage member adapted for introduction offluorocompound-containing gas thereto at a first end thereof for flowthrough the flow passage member to a second discharge end thereof; aheat source for heating the fluorocompound-containing gas during flowthrough the elongate flow passage member to a reaction zone at anintermediate portion of the elongate flow passage member between itsfirst and second ends; and a steam source arranged to inject steam intothe reaction zone of the elongate flow passage member.
 2. An apparatusaccording to claim 1, further comprising a cooler operatively thermallycoupled to the elongate flow passage member between the reaction zoneand the second end of the elongate flow passage member.
 3. An apparatusaccording to claim 1, wherein the heat source comprises a cartridgeheater.
 4. An apparatus according to claim 1, wherein the elongate flowpassage member is constructed as a throughbore passage in a blockmember.
 5. An apparatus according to claim 4, wherein the block memberfurther comprises a water flow steam generation passage therein, whereinsaid water flow steam generation passage terminates at a steam entrancecommunicating with the throughbore passage at the reaction zone.
 6. Anapparatus according to claim 4, wherein the block member furthercomprises a cartridge heater passage therein, and a cartridge heaterinstalled in the cartridge heater passage.
 7. An apparatus according toclaim 4, wherein the block member further comprises a water flow steamgeneration passage therein, wherein said water flow steam generationpassage terminates at a steam entrance communicating with thethroughbore passage at the reaction zone, and wherein the block memberfurther comprises a cartridge heater passage therein, and a cartridgeheater installed in the cartridge heater passage.
 8. An apparatusaccording to claim 4, wherein the block member comprises two matablyengageable half-sections.